Question

I was surfing the net looking for a nice effect for turning pages on Android and there just doesn’t seem to be one. Since I’m learning the platform it seemed like a nice thing to be able to do is this.

I managed to find a page here: http://wdnuon.blogspot.com/2010/05/implementing-ibooks-page-curling-using.html

- (void)deform
{
  Vertex2f  vi;   // Current input vertex
  Vertex3f  v1;   // First stage of the deformation
  Vertex3f *vo;   // Pointer to the finished vertex
CGFloat R, r, beta;
  for (ushort ii = 0; ii < numVertices_; ii++)
  {
    // Get the current input vertex.
    vi    = inputMesh_[ii];                       
    // Radius of the circle circumscribed by vertex (vi.x, vi.y) around A on the x-y plane
    R     = sqrt(vi.x * vi.x + pow(vi.y - A, 2)); 
    // Now get the radius of the cone cross section intersected by our vertex in 3D space.
    r     = R * sin(theta);                       
    // Angle subtended by arc |ST| on the cone cross section.
    beta  = asin(vi.x / R) / sin(theta);       

// *** MAGIC!!! ***
v1.x  = r * sin(beta);
v1.y  = R + A - r * (1 - cos(beta)) * sin(theta); 
v1.z  = r * (1 - cos(beta)) * cos(theta);
// Apply a basic rotation transform around the y axis to rotate the curled page.


 // These two steps could be combined through simple substitution, but are left
    // separate to keep the math simple for debugging and illustrative purposes.
    vo    = &outputMesh_[ii];
    vo->x = (v1.x * cos(rho) - v1.z * sin(rho));
    vo->y =  v1.y;
    vo->z = (v1.x * sin(rho) + v1.z * cos(rho));
  }  
}

that gives an example (above) code for iPhone but I have no idea how I would go about implementing this on android. Could any of the Math gods out there please help me out with how I would go about implementing this in Android Java.

Is it possible using the native draw APIs, would I have to use openGL? Could I mimik the behaviour somehow?

Any help would be appreciated. Thanks.

****************EDIT**********************************************

I found a Bitmap Mesh example in the Android API demos: http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/graphics/BitmapMesh.html

Maybe someone could help me out on an equation to simply fold the top right corner inward diagnally across the page to create a similar effect that I can later apply shadows to to gie it more depth?

Answer 1

I just created a open source project which features a page curl simulation in 2D using the native canvas: https://github.com/moritz-wundke/android-page-curl
I’m still working on it to add adapters and such to make it usable as a standalone view.

• EDIT: Links updated.
• EDIT: Missing files has been pushed to repo.